Electrical circuits



June s, 1928. 1,672,057

A. B. CLARK ELECTRICAL CIRCUITS Filed Sept. 1'7, 1924 2 Sheets-Sheet 1 INVENTOR L mRNEY June 5, 1928. 1,672,057

A. B. CLARK ELECTRICAL CIRCUITS Filed Sept. 17, 1924 2 Sheets-Sheet 2 IINVENTOR.

BY 7 WC ATTORNEY Patented June 5, 1928'.

units!) STATES I r 1,672,057 PATENT OFFICE.

ALVA Benson CLARK, or naooxnya, new YORK, assmnoa 'ro aim-mom ml mom: am) ramemn compan a coaroaa'rxon or rmw You ELECTRICAL cmcurrs.

Application filed September 17, 1o24. Serial m. maoa.

The object of my invention is to provide a new and improved method for economizing in the use of apparatus to produce desired changes in electric currents. Another 5 object of my invention is to provide apparatus for modifying an electric current in a desired manner with eifective use of the elements of the apparatus. Another object of my invention relates to reducing the amount of apparatus in an electrical net- Work by employing reflection and utilizing the same network for transmission two ways. Another object of my invention is to amplify the current advantageously in connection with such reflection. These and various other objects of my invention will become apparent on consideration of a specific example which'Ihave chosen for disclosure in the following specification and claims taken with the accompanying drawings. It will be understood that the following specification relates to this example of the invention, leaving the invention to be defined in the claims. Referring diagram il ustrating; a two-way wire and wireless transmission system in which my invention finds useful application; Fig. 2 is a diagram of a delay circuit that may be employed in the system of Fig. 1; and

Fi 3 is a diagram of a delay circuit emying my invention.

In the system shown in Fig. 1, W, and E,

, are two telephone stations, each with a transmitter and receiver, and the apparatus lying between these stations is adapted to transmit speech both ways, partly by wire and partly by wireless. The normal condition ofv the system when not in use involves a closure of the shunt 21 at the back contact of the amplifier-detector unit relay A When E speaks, the transmission is into the hybrid coil H which connects with a four-wire line, as shown. Thence the voice currents g0 throughrepeaters R and over the wire line L to the. radio transmitter T, from which the radio waves are received by the radio receiver B0,. Thence transmission is over the line L through the repeaters R to the hybrid coil H, and thence to the station W,.

The transmission, as thus described, is not afl'ected by the shunt 22, because it is open at the front contact of the relay system A,. The symbol A, indicates-an amplifier-detecto the drawings, Figure 1 is a tor unit relay which is operated by the voice current inthe line L and, while the voice currents are being carried from the station E, to station W,, the relay A, is energized and closes on its front contact the shunt 23, thus inhibiting transmission from W, to E,.

If the subscriber at- W, speaks while the system is not in use, the voice currents in t e primary windings of the hybrid coil H, will occasion voice currents in the line L, and repeaters R which will go to the amplitier-detector unit relay. A, and oen the shunt 21 and closes the shunt 22. T e opening of the shunt 21 will make the system operative for transmission from W, to E,, and the closing of the shunt 22 will make it inoperative for transmission the other way. a

In order that the transmission from W, to E, may not be mutilated, the delay circuit D .is interposed. This is so arranged that, while the initial voice current waves are plassing through D on the way from W, to

the relay A will have time to operate.

so that when these wavesreach the output of D the" shunt 21 will have been opened, and they will pass in unmutilated condition on over the line L, to the transmitting station W, and thence in an obvious manner to the subscriber at E,.

It will be seen that, although the system is a four-wire system, it is so arranged at station W that on] one pair is operative at one time. Norma ly the pair from E, to W, will be operative in virtue of the normally open condition of the shunt 22, and the air from W, to IE, will be inoperative because of the closure of the shunt .1. When E, talks, then as long as he talks continu'ously he sustains this condition by virtue of the energization of relay A, which closes the shunt 23 and prevents energizing relay A, which wouldclose the shunt 22. W, can get possession of the line only when E, is

not talking and when, accordingly, the relay A, is not energized. Then when W, talks, the relay A, is energized thus opening the shunt 21 and closing the shunt 22 thereb preventing energization of relay A, an preventing the closure of the shunt 23, and

this condition maintains as long as W, talks continuously. I

In this way interference, due to echoes or singing around the four-wire circuit, is prevented. -A delay circuit such as indicated by the character D in Fig. 1 is shown more in detail in Fig. 2. It consists of a large number of series coils L and alternately disposed shunt condensers C, the terminal condensers having appropriate capacity values differing from the others as indicated by the character. C To get the necessary dela the number of sections in the network of ig. 2 may need be as great as several hundred.

To reduce the quantity of apparatus involved, I construct the network D in accordance with Fig. 3, instead-of Fig. 2. It will first be described on the assumption that the switches S are open. The voice currents coming in from the left to the terminals 2i divide equally, half going to the network N and half to the network D so that there is a balance in the secondary windin of the hybrid coil H, and, as described t us far, there is no current to the output terminals 25.

The network N is designed so that there is no reflection. of the current passing into it, and its energy is entirely absorbed therein. It is designed to balance a network extending to infinity whose sections are like those of network D. The network D consists of'sections like the sections of Fig. 2 except that there are only half as many. The current wave entering the network D from the left traverses it to the right and is reflected at SS. and goes back entering the hybrid coil, as indicated by the arrow 26. Its energy is divided, partly going out at the normal input terminals 24 and partly at the normal output terminals 25.

While there is no reflection between the hybrid coil and the network D for currents entering the network D at this place, there is complete reflection at the extreme unconnected end of the network D, that is at SS, and thus it will be seen that the network D is completely traversed twice, and since it has ha f the number of sections of Fig. 2, the wave passes through the same number of sections as in Fig. 2.

Referring to Fig. 2, if there is an odd number of condensers C and if the middle condenser is replaced by two condensers in parallel, as shown at 27, then it will be seen that if the reflection can be accomplished at 27, the completely reflected wave will have traversed the same number of sections and Wlll have been subjected to the same modifying influence as the completely transmitted wave would have been. This is the prin ciple of Fig. 3 as compared with Fig. 2, as

described thus far, that is with switches S open.

Now let switches S be closed. Accordingly, the wave currents that have passed once through the network D, instead of being immediately reflected as before, will now enter the 21-type repeater at its input terminals 31. In the usual manner for such a repeater, the energy willdivide, part entering the outputcircuit of the amplifier A and being absorbed and part entering the in put circuit and being amplified and going. through the output-circuit to the windings 32 of the hybridcoil. The consequent induced currents in the windings, 33 divide, half going to the balancing network N and half through the network D from right to left, as viewed in Fig. 3.

In virtue of the amplification at A, a much larger current enters at 26 in Fig. .3, and a correspondingly-larger current is put on the line at the terminals 25, as compared with i when switches S areopen. Thus the amplifier A may be made to compensate for attenuation, if any, in the network D, and

in any case the current is advantageously I 7 ing made the complete trip. This wave has a tendency to impair the quality of the speech transmitted through the circuit, and

it is therefore desirable to' keep it small I relatively to the main wave. It will be seen that this is accomplished by my invention,

ffioii it is the main wave only that is ampli- It is impracticable to manufacture coils and condensers. quite free from dissipation and therefore, the waves which traverse the network are inevitably attenuated in some degree, and obviously the main wave which traverses the whole network twice will be attenuated more than the advance wave, due to partial reflection that has just been mentioned. But by my invention, the amplification of the main wave com nsates for its greater attenuation compare to the advance internally reflected wave.

On the other hand, there is a limit to thedegree of amplificationthat is advantageous, for after amplification, there will be small partial internal reflections back toward the repeater, and these waves will in turn be amplified and will follow through behind the main wave and interfere with the quality of the speech if the amplification ratio is made too great. 7

While I have explainedmy invention in relation to a delay circuit, it will readily be understood that this principle will be found applicable for the case 01 an circuit in which it is desired to make a c ange'in the current at the output terminals as compared with the current at the input terminals.

1. The method of producing a desired degree of change in electric'wave currents between a pair of input terminals and a pair of output terminals which consists in sending the currents from the input terminals without immediate efiect on the output terminals throu h a network that produces half the desired c ange, amplifying the currents, and reflecting them back through the said network to complete the desired change, and making the reflected currents effective on the output terminals of the system.

2. In combination, va hybrid coil with outi put terminals unaffected directly by current introduced at the input terminals, a network to receive cur-rent from the in at terminals, and a 21-type repeater to ampllfy and reflect the current back through said network, the system being adapted to make the reflected cuil rent waves eflective on-the output termina s. I

3. In combination, a hybrid coil with a pair of input terminals and a pair of output terminals, an absorbing network and a re flecting network balanced against each other with respect to one said pair of terminals, and a 21-type re ater associated with said reflecting networ 4. In combination, a hybrid coil with input and output terminals and two networks to which the input currents divide, one network being completely absorbent and the other network havin a 21-ty repeater at its distal end adapte to amplify and reflect the waves transmitted through it whereby these waves, after twice traversing the last mentioned network and being amplified, become effective on the output terminals.

5. In combination, a delay network havi at one end thereof two conju ate pairs 2% terminals, means to establish t e conjugate relation between them, and a 21-type repeater at the other end of the said network.

6. The method of transmittin a current with delay through a network aving two conjugate pairs of terminals which consists in putting the current in at one lair of terminals andtransmitting it over t e network and reflecting it with amplification back through the networkto the other pair of so terminals.

In testimony whereof, I have signed my name to this specification this 15th day of September, 1924.

ALVA BENSON CLARK. 

